1. Field of the Invention
The present invention relates to an extruding device for molding honeycomb structural bodies made of a molding material such as a ceramic or a resin. In particular, the invention relates to devices for producing honeycomb structural bodies having curved shapes.
2. Related Art Statement
In general, a plastic molding material such as a ceramic or a resin is passed through a special die of an extruding machine, and is continuously extruded from the die to produce an extruded honeycomb structural body. When the honeycomb structural body is extruded by using such an extruding machine, an extruded body having a straight shape is formed in an extruding direction because the molding is continuously extruded by the molding machine.
For this reason, although extrusion of curved honeycomb structural bodies with use of an extruding machine can be imagined as a concept, it is not easy to extrude a honeycomb structural body having a curved shape in an actual process.
Japanese patent application Laid-open No. 57-78,965 discloses such a process for extruding curved honeycomb structural bodies. In this process, the lengths of passages formed in a die of an extruding machine in the form of a honeycomb are varied, so that the curved honeycomb structural body is formed by utilizing the feature that extruded flow resistance of the molding material becomes greater as the length of the passage increases. In this process, tapered slanting surfaces are formed on respective slit-forming portions of a molding die so that the lengths of the flow passages are variable with such tapered slanting surfaces and that the molding is bent on a side of an extruding outlet, depending upon the magnitude of the flow passage resistance, toward a direction in which the flow passage resistance becomes greater.
However, this conventional process has the following problems.
(1) Since the extruding machine has a structure in which the tapered slanting surfaces are formed on the molding die, it is difficult to work the die, and the actual die-producing process suffers troublesome working steps and results in costly dies.
(2) Since the passed amount of the body becomes non-uniform depending upon the lengths of the passages of the die, the thickness of inner walls of the resulting molding becomes non-uniform, with the result that the moldings obtained are likely to have non-uniformity and poor quality as structural bodies.
(3) The flow rate of the body at the side of the outlet needs to be finely adjusted on molding, but this fine adjustment in the die is difficult when considered from working operation.
(4) Further, in order to obtain different kinds of honeycomb structural bodies having largely differing radii of curvature (R), a plurality of molding dies having different specifications are required, so that it is difficult to obtain curved honeycomb structural bodies having different radii of curvature by using a single molding die.